Admixture of SiO2 to Suppress TiO2 Crystallization

Crystallization of glassy TiO2 films used in optical coatings can be a problem in high power applications and may be a major limitation to the laser damage threshold. An attempt to suppress such crystallization involved mixing small amounts of SiO2 into TiO2 during the ion-beam sputter deposition process. An admixture of 5% SiO2 increased the crystallization onset temperature, determined by Raman spectroscopy, by approximately 150°C. The refractive index was relatively unaffected by the addition of 5% SiO2, dropping from 2.42 to 2.38. Optical loss, which shows a sharp increase near 350°C for pure TiO2, did not increase measurably for the films with SiO2 admixture of 5% or greater.